1. Field of the Invention
This invention relates to a process for fixing (tanning) natural tissue heart valve prostheses.
2. Description of the Prior Art
It is known that the tensile properties and antigenic reaction of a natural tissue heart valve prosthesis may be improved by fixing the valve before it is implanted. Glutaraldehyde is commonly used as a fixing agent.
Commonly owned U.S. Pat. Nos. 3,983,581 and 4,035,849 describe a fixing procedure in which porcine valves are fixed in glutaraldehyde with the valve cusps held in a closed position by applying hydraulic pressure to the ventricular side of the valve.
Thompson, F J and Barratt-Boyes, B G, "The Glutaraldehyde-treated Heterograft Valve", Journal of Thoracic and Cardiovascular Surgery, Vol 74, No 2, pp 317-321, August 1977, report in vitro tests comparing heterograft valves that were apparently fixed in glutaraldehyde with the cusps closed under "physiological pressure" with antibiotic-treated homograft valves. The heterograft valves were reported to remain closed at zero pressure across the valve and to not fully open until the flow rate (Piper's solution at 37.degree. C.) through the valve was greater than 10 liters per minute. The article concluded that the cusps of the heterograft valve do not open as freely as those of the homograft valve and that such performance may be responsible for the rather high pressure drop across heterograft valves reported by prior investigators.
The main object of the invention process is to make natural tissue heart valve prostheses whose cusps open more freely. Such valves are characterized by improved in vivo hydraulic performance.